Due to the rich color of the latex paint, the light and dark colors can be selected at will, the decorative effect is good, and the use period is long. The architectural coatings using acrylic emulsion as the film-forming material play an increasingly important role in urban dressing. As an important component in latex paints, the choice and use of organic plastic pigments directly affect the color retention of latex paints, and an understanding of pigment properties and applications can guide the production of high-quality latex paints. Organic pigments are not affected by physical and chemical factors during use. They are generally insoluble in the medium used and always exist in their original crystalline state. The coloring of organic pigments is achieved by selective absorption and scattering of light.
1. Pigment paste
The application of organic pigments in architectural coatings is mainly done through pigment pastes. Color paste is a highly dispersed pigment preparation. The organic pigment content in the color paste is 30% -50%, and the inorganic pigment content is 60% -75%; the higher the pigment content, the smaller the adverse effect on the color paste system. Requires good dispersion of color paste, good compatibility with water-based polymer emulsion, free of binders, ethylene glycol and harmful heavy metal ions; requires good batch uniformity of color paste, and coloring error control within ± 5% (Higher requirement ± 3%); It is required that the color paste has good stability, at least 2a storage period. It is required that the color paste can be mixed with the latex paint in any proportion. The composition and production conditions of various color pastes vary according to the nature of the pigments contained.
2. Application of pigment paste
Pigment paste is widely used in various interior and exterior wall architectural coatings (latex paint), water-based industrial coatings, water-based wood coatings, etc. The use of color paste in latex paint is a mixture of two dispersion systems. The pigment in the color paste is dispersed in water under the action of surfactant A. The performance and quantity of the surfactant determine the pigment content, degree of dispersion and stability; and the film-forming substance (resin) in the latex paint is active on the surface Dispersed in water under the action of agent B, the nature and quantity of surfactant determine the average particle size, gloss and stability of latex paint. If the compatibility of the two dispersion systems is not good, the following problems will occur:
①If the type of dispersant used in the color paste does not match, the dispersant will react with each other and break the emulsion; ②If the amount of the dispersant used in the color paste is not enough, it will lead to poor stability of the architectural coating; ③If the colorant uses the dispersant If the quantity is too large, the water resistance and drying performance of the coating film will be poor; ④ If the pigment agglomerates, it will lead to a decrease in the coloring power of the paint, a change in hue, a reduction in hiding power, a decrease in gloss, poor fluidity, and poor leveling.
3. Precautions for using pigment paste
Choose to use high-quality pigment paste. The color paste should have a stable hue and coloring power, and have good light resistance, weather resistance, acid and alkali resistance; it must be compatible with the coating system and can be mixed with each other; stable storage, no precipitation, no flocculation, no drying Not frozen; reasonable price-performance ratio.
Before use, the compatibility test of color paste and paint should be done, and fully stirred to avoid uneven color paste state (layering, density difference between upper and lower layers) caused by temperature change or long storage time during transportation, which affects the amount of addition The accuracy; it is best to add color paste while stirring the paint, and the paint should be stirred evenly. The color paste is best added directly and cannot be added after dilution with water. If an incomplete bucket of color paste is used at one time, the cover must be closed immediately after use to avoid contamination of the surface of the color paste or dry and powdery surface of the color paste due to water evaporation, which will affect the next use.
The maximum addition amount of color paste in latex paint should be controlled within a reasonable range, beyond the reasonable range will destroy the balance of the latex paint system, will seriously affect the durability of the coating film, especially water resistance. The maximum amount of organic pigment paste should not exceed 8%, and the maximum amount of inorganic pigment paste should be within 15%. When producing exterior coatings, try to choose color pastes with good light resistance, weather resistance and alkali resistance. Generally speaking, iron oxide pigment pastes have better alkali resistance than organic pigment pastes.